We've observed this also, with systems with large spatial extents and
containing D orbitals. Localized systems work fine, systems without D
orbitals of any extent work fine. This is occurring in solution for
us.
MZ
On Fri, Sep 28, 2012 at 10:09 AM, Gerald Monard
<gerald.monard.univ-lorraine.fr> wrote:
> Hi,
>
> I run some tests on your files. It seems indeed that only PM6 crashes at
> some point. Other semiempirical hamiltonians do not crash (I tested AM1,
> PM3, PM3-PDDG, and RM1). May be there is a problem in the PM6 potential
> energy surface describing your system.
>
> Sincerely,
>
> G. Monard.
>
> On 09/28/2012 10:58 AM, Gerald Monard wrote:
>> Hi,
>>
>> IMHO, I'm not sure that it is really a SCF convergence problem in your case.
>> Your system is a charge separated system ( (CH3NH3^+)2 + NH4^+ (SO4H^-)2
>> ) that you try to simulate in gas phase at T=800K. There is a really
>> great chance that during an QM-MD, your system will blow up at some
>> point. In a certain chemical sense, I am not sure that this is something
>> wrong.
>>
>> I made some quick tests with your system (minimization before running
>> the MD, 300K instead of 800K, vrand=10 instead of 100, etc.), but at
>> some point there is always a proton transfer between an amine group and
>> a sulfate, then the system explodes because of the energy released.
>> If your system was soaked into a aqueous solvent for example, I am
>> pretty sure that this would not happen.
>>
>> Sincerely,
>>
>> G. Monard.
>>
>>
>> On 09/28/2012 01:45 AM, Wei Lin wrote:
>>> Hi Everyone,
>>>
>>> I tried to run MD simulation with PM6 Hamiltonian for a small charged
>>> cluster contained d-orbital element. After ~ 38 steps of simulation,
>>> the system blows up with error message as follows:
>>>
>>> QMMM: WARNING!
>>> QMMM: Unable to achieve self consistency to the tolerances specified
>>> QMMM: No convergence in SCF after 1000 steps.
>>> QMMM: Job will continue with unconverged SCF. Warning energies
>>> QMMM: and forces for this step will not be accurate.
>>> QMMM: E = -0.6307E+06 DeltaE = 0.1152E-01 DeltaP = 0.3365E-02
>>> QMMM: Smallest DeltaE = 0.3550E-03 DeltaP = 0.2442E-02 Step = 787
>>>
>>> Then, I set up another simulation for the same system with Gaussian
>>> interface. The simulation runs well.
>>>
>>> Andy Goetz suggested that can be related to SCF convergence algorithms
>>> in sqm. I am wondering if anyone knows how to overcome this problem.
>>>
>>> The mdin (both in sqm and Gaussian interface), inpcrd, prmtop and run
>>> files are attached.
>>>
>>> Thanks,
>>> Wei
>>>
>>>
>>> _______________________________________________
>>> AMBER mailing list
>>> AMBER.ambermd.org
>>> http://lists.ambermd.org/mailman/listinfo/amber
>>
>
>
> --
> ____________________________________________________________________________
>
> Prof. Gerald MONARD
> Theoretical Chemistry and Biochemistry Group
> SRSMC, Université de Lorraine, CNRS
> Boulevard des Aiguillettes B.P. 70239
> F-54506 Vandoeuvre-les-Nancy, FRANCE
>
> e-mail : Gerald.Monard.univ-lorraine.fr
> tel. : +33 (0)383.684.381
> fax : +33 (0)383.684.371
> web : http://www.monard.info
>
> ____________________________________________________________________________
>
>
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Received on Fri Sep 28 2012 - 09:00:04 PDT
